Seat adjuster track mechanism



p 6, 1961 c. F. KRAMER 3,001,835

SEAT ADJUSTER TRACK MECHANISM Filed July 20, 1959 g CLARENCE E KRAMER gINVENTOR. a nf 3 ,6? '4 BY M .A TTOPNEKS' United States Patent 3,001,835SEAT ADJUSTER TRACK MECHANEM Clarence F. Kramer, Birmingham, Mich.,assignor to Ford Motor Company, Dearborn, Mich., a corporation ofDelaware Filed July 20, 1959, Ser. No. 828,387 3 Claims. (Cl. 308-6)This invention relates generally to adjustable seats for motor vehicles,and has particular reference to a seat adjuster mechanism having aslidable track unit supporting the vehicle seat for fore and aftmovements.

Seat adjuster mechanisms embodying a slidable track unit providing thefore and aft adjustment and positioning of the seat are well known tothe prior art. In general, the slidable track unit comprises a pair ofsubstantially U-shaped channel track members, one invertedlyencompassing the other. The track members are provided with laterallyextending, race forming flanges thereon in complementary relationship toeach other. A bearing element, usually a small diameter ball, isinterposed between each pair of flanges to provide lateral bearing meansbetween the track members. A center bearing element, a ball somewhatlarger in size than the lateral bearing elements, is interposed betweenthe opposed base portions of the track members. Usually, the sidebearing elements and the center enlarged bearing element are maintainedin a predetermined relationship to one another by a suitable cagedevice. One of these bearing element assemblies is positioned at eachend of the track unit.

In a conventional structure the center bearing element or ball whilerolling on the lower track member supports the vertical load of thevehicle seat and its occupants, while the lateral bearing elements orballs merely provide lateral stability.

It is an object of the present invention to provide an improvedconstruction and arrangement of the track unit in which a part of thevertical load carried by the center bearing element or ball isdistributed to at least one of the bearing elements or balls between thelateral flanges of the track member. In a conventional track unit, theopposed base portions of the track members are both either flat or oneof them is provided with a curved surface complementary to the ballsurface. In the structure embodying the present invention, one ballengaging base portion, preferably that of the upper track, is curvedoppositely to the curvature of the ball, thereby providing an unstablecondition. Because of this deliberately created unstablecondition, thetendency of the track to shift laterally to the extent of the tolerancmbeween the lateral bearing elements and the associated race formingflanges results in a vertical component of force being exerted on atleast one of the balls forming the lateral bearing elements. Thisresults in a reduction of the load on the center ball element.

Other objects and advantages of this invention will be made moreapparent as this description proceeds, particularly when considered inconnection with the accompanying drawings, wherein:

FIG. 1 is a perspective view, in part sectional, of one track unit of anadjustable seat mechanism incorporating the present invention;

FIG. 2 is a sectional view taken substantially through line 22 of FIG. 1looking in the direction of the arrows; and

FIG. 3 is an enlarged cross sectional view taken substantially on theline 33 of FIG. 2 looking in the direction of the arrows.

Referring now to the drawings, and particularly to FIG. 1, there isillustrated one of the two seat track units located at each side of thevehicle seat (not shown) and Patented Sept. 26, 1961 "ice supporting thelatter for 'fore and aft adjustment. The illustrated unit, generallydesignated 11, is the one usually found beneath the left or drivers sideof the vehicle seat, as will be more fully explained. The right-handunit (not shown) is substantially the same as the illustrated unit. Theminor differences between the two do not affect the present inventionand only the one unit will be described in detail.

Much of the structure illustrated follows conventional practice. A briefdescription of the details should suflice for an understanding of thepresent invention.

In general, the seat track unit 11 comprises a lower track member 12 andan upper track member 13. Each of the track members is a substantiallyU-shaped channel member. The lower track member 12 is provided with abase portion 14' and upwardly extending leg portions 15 and 16 at eachside of the base portion. Each of the leg portions 15 and 16 terminatesin a laterally extending, outwardly curved flange 17 and 18,respectively.

The upper track member 13 is provided with a base portion 19 anddownwardly depending leg portions 21 and 22 at each side thereof. Eachof the leg portions 21 and 22 terminates in a laterally extending butinwardly curved flange 23 and 24, respectively.

As seen in FIG. 3, the upper track member 13 invertedly encompasses thelower track member 12. Each pair of flanges 17 23 and 1824 arecomplementally curved to form races receiving bearing elements in theform of small balls 25. In a conventional seat track structure thefunction of the small balls 25 is to provide lateral bearing meansbetween the channel members or track members 12 and 13, and, thus, tocontrol the lateral stability of the seat adjuster mechanism.

The vertical load on the upper seat track 13 is transmitted to the lowertrack 12 through bearing elements in the form of balls 26 somewhatlarger in diameter than the balls 25. Each pair of side balls 25 andassociated centrally positioned balls 26 are retained in predeterminedlateral position or alignment by means of a bearing cage 27 of anyconvenient form. It will be understood that there are generally two ofthese ball and track assemblies, one located at each end of the trackunit.

The lower track 12 is supported on suitable front and rear brackets 28and 29, respectively, on the floor of the vehicle body. The upper track13 is provided with the necessary support bracket 31 at the rear thereofand the necessary retaining devices, such as the device 32 shown at thefront of the bracket, for supporting and securing the frame of thevehicle seat. An elongated tension or assist spring 33 is provided toexist in forward and slightly upward movement of the seat. The springextends between a flange 34 on the fixed front support bracket 28 andthe edge wall of an aperture 35 in the seat support bracket 31 carriedon the movable upper track 13.

Any convenient type of latching device may be provided to hold the uppertrack 13 in adjusted position relative to the lower track 12. Asillustrated, the latching device comprises a latch plate 36 pivotallymounted on the upper surface of the upper track member 13. The latchplate 36 is provided at the side 37 thereof with pawl elements (notshown) engageable with rack elements (not shown) on the side of thelower track member. A tension spring 38 is provided which extendsbetween a latch plate extension 39 and a suitable aperture in the sidewall of the bracket 31. The spring 38 continually urges and holds thelatch plate in latching position. A suitable hand lever 41 is providedwhen it is desired to retract the pawl elements from the rack elementspermitting the upper track member '13 to be adjusted relative to thelower track member 12. The hand lever 41 is usually provided only on thelatch plate mounted on the track unit 11 beneath the drivers side of thevehicle seat. The track unit mounted at the opposite side of the vehicleseat is provided with a similar latch plate except that the latter isadapted to be actuated by remote control through the medium of a cable42 extending between it and the latch plate operated by the handle 41.

The feature which distinguishes the seat track unit 11 embodying thepresent invention over the conventional seat track units as abovedescribed relates to the vertical load carrying balls 26 and theirassociate sections of the upper track member 13. In a conventional seattrack the base portion 19 is either flat or, as it would appear from theinside, laterally curved to provide a groove or recessed track in whichthe ball would roll, in a relative sense. The groove might have a crosssectional radius substantially equal to or somewhat larger than theradius of the ball 26. Whether flat or so grooved, the entire verticalload carried by the track is concentrated on the balls 26. The smallerside balls 25 merely function to provide lateral stability.

In carrying out the present invention, the conventional groove is turnedinside out. As best seen in cross section in FIG. 3, the ball 26 is inengagement with a convexly curved, as it appears from the inside,centrally located elongated raised section 43 of the base portion 19.The relative length of the raised section 43 to the length of the uppertrack member 13 is illustrated in FIGS. 1 and 2. It will be noted thatthe base portion 19 of the upper track member 13 is provided with thelongitudinally extending raised sections 43' at each end thereof. Eachraised section 43 is at each of its ends provided with semisphericalknolls 44. The knolls 44, which project deeper into the channel member13 than the raised sections 43 proper, act as stops which in partcontrol the range of movement of the upper track member 13 over theballs 26. In this regard, it will be noted that the studs or rivets 45securing the lower track 12 to the support brackets 28 and 29,respectively, are provided with enlarged head portions eflective tolimit the distance each ball 26 may roll relative to the lower track.

To complete the description of the physical details of the seat trackunit 11, it should be noted that wear strips 46 are provided on whichthe balls 26 are adapted to roll. One of these wear strips 46 extendsbetween each pair of stops 45 on the lower track member 12. Each of thewear strips 46 is an elongated member, made of a resilient material suchas spring steel. Each wear strip is preferably anchored at only one endby the same rivet or stud 45 securing the track member to the supportbracket.

The wear strips 46 have a function other than merely providing a wearresistant surface for the balls 26. This second function forms animportant feature of the present invention. As best seen in FIG. 3, eachwear strip 46 is provided with a concave lateral curvature opposing theconvex lateral curvature of the track section 43. In addition, eachstrip member 46 is slightly longitudinally bowed, its free end when notunder pressure from a ball 26 being flexed upwardly from the surface ofthe track member 12.

The manner in which the seat track units embodying the present inventionoperate may best be explained with reference to FIG. 3. It will bereadily understood that as the seat is shifted fore or aft, each ball 26rolls beneath the track member 13 and over the lower track member 12. Ina conventional seat track unit, the only function of the side bearingelements or balls 25 is to provide lateral stability of the uppermovable track member 13 relative to the fixedly supported track member12. However, as is readily apparent from FIG. 3, in the presentconstruction and arrangement, the seat track 13 has a precarious perchon the balls 26. Assuming no lateral clearances between the balls 25 andtheir associated flanges, the line of contact of each ball 26 and baseportion 19, that is, the curved section 43* of file latter, would lie onthe vertical center line of the ball. Stated in another way, the crestof the convexly curved section 47 would be in tangential contact withthe ball 26 at a surface or peripheral point lying on the verticalcenter line of the ball. In practice, there are always sufficientdeviations of clearances resulting from manufacturing tolerances whichpermit sufiicient lateral play between the two tracks 12 and 13 toresult in the upper track slipping to one side of the vertical centerline of the ball 26. There is, of course, a reaction force acting on theball 26. Because of the concave curvature of the wear strip 46 and theresistance to downward deflection resulting from the longitudinallybowed form of the strip member, the ball 26 tends to remain centered orstabilized relative to the lower track member.

The slight lateral shift of the upper track member 13 resulting from itsunstable relationship to the balls 26 results in some of the verticalload being shifted to the balls 25 on the side of the vertical centerline of the ball 26 opposite to that to which the upper track curvedsection 43 has shifted. For example, if the direction of the lateralshift of the upper track '13 is to the left of the vertical center lineof the ball 26, as viewed in FIG. 3, the force causing such shiftresults in a force couple tending to raise the flange 24 of the legportion 22 of the track member 13. The ball 25 between the flange 24 andits associated flange 18 is then subject not only to the usual laterallyor horizontally acting components of force, as found in conventionalseat track units, but is also subject to vertical force components.These vertical force components, in eflfect, are a partial distributionof the load or vertical forces acting directly on the associated ball26.

The result of the foregoing is a distribution of the load over a greaternumber of balls with a resultant greater ease of operation. A secondaryresult is the take-up of all lateral clearances. Instead of the uppertrack being able to shift from side to side laterally as it moveslongitudinally of the lower track, it exerts a lateral thrust primarilyagainst the balls carrying the vertical load and does not shift from oneside of the vertical center line of the ball 26 to the other. The resultis a much smoother operating seat track unit.

It will be understood that the invention is not to be limited to theexact construction shown and described, but that various changes andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the appended claims.

What is claimed is:

1. In a seat track unit comprising an upper and a lower channel member,said upper channel member invertedly encompassing the lower channelmember with their base portions in opposed spaced relationship, saidmembers being provided with complementary laterally extending raceforming flanges thereon, ball means interposed between said flangesproviding lateral bearing means between said channel members, said upperchannel member being shiftable laterally relative to said lower channelmember to the extent of the clearances between said ball means and saidrace forming flanges, and a ball element interposed between said baseportions maintaining said channel members in vertical spacedrelationship, said upper channel member being provided with a convexlylaterally curved ball element engageable means, the relationship betweensaid upper channel member base portion means and said ball elementcreating an unstable condition whereby said upper channel member shiftslaterally to take up said clearances and a part of any vertical loadcarried by said ball element is distributed to the lateral bearing meanson at least one side of said channel members.

2. In a seat track unit comprising a pair of substantially U-shapedchannel members, one invertedly encompassing the other, said membersbeing provided with complementary laterally extending race formingflanges thereon, ball means interposed between said flanges providinglateral bearing means between said channel members, said upper channelmember being shiftable laterally relative to said lower channel memberto the extent of the clearances between said ball means and said raceforming flanges, and a ball element interposed between said baseportions maintaining said channel members in vertical spacedrelationship, said upper channel member having a convexly laterallycurved ball element engageable means integral therewith and the lowerchannel member base portion a conoavely laterally curved ball elementengage- 1O able means supported thereon, the relationship between saidupper channel member base portion means and said ball element creatingan unstable condition whereby said upper channel member shifts laterallyto take up said clearances and a part of any vertical load carried bysaid ball element is distributed to the lateral bearing means on atleast one side of said channel members.

3. A seat track unit according to claim 2 in which a cage means extendsbetween said ball means and ball element to maintain the same inpredetermined longitudinal and lateral relationship relative to oneanother.

References Cited in the file of this patent UNITED STATES PATENTS2,307,305 Saunders Jan. 5, 1943 FOREIGN PATENTS 725,218 Great BritainMar. 2, 1955

